How hot is too hot for the human body?

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For study published in Nature Climate Change in 2017, Mora and his team analyzed hundreds of extreme heats around the world to determine which combinations of heat and humidity are most likely to be deadly and where those conditions are likely to occur in the future.

They found that while today about 30% of the world’s population is exposed to a deadly combination of heat and humidity for at least 20 days each year, that percentage will increase to almost half by 2100, even with the most drastic reductions in greenhouse gas emissions.

Other researchers have found that climate change creates extreme heat waves hundreds of times more likely and provocation over a third heat-related deaths. We are changing our planet – what are the limits of what we can handle?

Cooling

As warm-blooded mammals, humans have a constant body temperature, about 98 ° F (37 ° C). And our bodies are designed to work pretty well at that temperature, so there’s a constant balance between heat loss and heat gain.

Problems start when our bodies can’t lose heat fast enough (or lose it too quickly in the cold, but for now let’s focus on heat). When the temperature of your core gets too hot, everything from organs to enzymes can be turned off. Extreme heat can lead to major kidney and heart problems and even brain damage Liz Hanna, a former public health researcher at the Australian National University, who studies extreme heat.

Your body works to maintain a baseline temperature in hot environments, mostly using one powerful tool: sweat. The sweat you create evaporates in the air, sucking heat from your skin and cooling you.

Moisture cripples this way of cooling – if it is so humid that there is already a lot of water vapor in the air, sweat cannot evaporate so quickly, and sweating will not cool you down so much.

Extreme heat can lead to major kidney and heart problems and even brain damage.

Researchers like Mora and his team often use measures like the heat index or temperature of a wet bulb to consider how the interaction of excessive heat and humidity works. This way they can focus on a single number to identify non-living conditions.

The heat index is an estimate you’ve probably seen in weather reports; it takes into account both heat and humidity to represent how the weather feels. The temperature of a wet bulb is literally what a thermometer measures if a wet cloth is wrapped around it. (The temperature in the forecast is technically the temperature of a dry bulb because it is measured with a dry bulb thermometer.) The temperature of a wet bulb can estimate what temperature your skin would have if you were constantly sweating, so it is often used to approximate people to price extreme heat.

A wet bulb temperature of 35 ° C or about 95 ° F is pretty much the absolute limit of human tolerance, he says Zach Schlader, a physiologist at Indiana University Bloomington. Above that, your body will not be able to lose heat from the environment efficiently enough to maintain a basic temperature. This does not mean that the heat will kill you immediately, but if you cannot cool down quickly, damage to the brain and organs will begin.

The conditions which can lead to a humid bulb temperature of 95 ° F varies greatly. Without wind and sunny skies, an area with 50% humidity will hit a humid bulb temperature that cannot be maintained at around 109 ° F, while in mostly dry air temperatures would have to reach a maximum of 130 ° F to reach that limit.



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